1. Field of the Invention
The present invention relates to a technique for preventing yellowing of an article (a medium on which a photographic image is formed, a printing medium on which normal printing is performed, such as a label, or an elastic microporous substance or swellable microporous substance or an article partially having such a microporous substance) having a microporous site, and particularly to a recording medium, which can achieve high image quality suitable for ink recording using aqueous inks and has a novel anti-yellowing agent having anti-yellowing capability over a long period of time, and a production process and a storing method thereof. The present invention also relates to an ink-jet recording medium, which has a function of preventing yellowing on white portions upon storage in a file without impairing ink recording properties when a microporous site is comprised of an alumina hydrate and can exhibit anti-yellowing performance over a long period of time, to say nothing of a physical distribution and storage period during which it is transported overseas by marine transport after its production to be sold, a production process thereof, and a storing method suitable for the prevention of yellowing.
2. Related Background Art
Many ink-jet recording methods comprise ejecting fine droplets of a liquid (recording liquid) for recording, such as an ink, by various working principles to apply them to a recording medium having a microporous site, thereby printing images, characters and/or the like of high image quality, and printers using an ink-jet recording system have come to be extremely preferably used with the spreading of digital cameras, digital video cameras, scanners, personal computers and the like. An ink-jet recording medium is required to permit forming an image having high quick-drying property, excellent coloring of a colorant and high surface glossiness and resolution. As a recording medium capable of providing an image comparable with a silver salt photograph, an ink-jet recording medium using a fine inorganic pigment (silica, alumina or the like) and a binder thereof to provide, as an ink-receiving layer having a high voidrate, a microporous site in the form of a layer on a support is put to practical use.
Patent Document 1 describes that an alumina hydrate is preferred as a material for forming an ink-receiving layer because it has a positive charge, and so fixing of a dye in an ink is good to provide an image having excellent coloring. Among alumina hydrates, an alumina hydrate having a pseudoboehmite structure is more preferred because it has good dye adsorptivity, ink absorbency and transparency. However, when a recording medium provided with a porous layer as an ink-receiving layer is stored in a file after printing on the recording medium, white portions of the recording medium may be yellowed with time in some cases. In such a recording medium having the colorant-receiving layer of the porous structure, it is thus a very important property to prevent yellowing of the white portions. It is known that since the microporous site of the recording medium of such a structure as described above has a great number of fine voids, a phenolic antioxidant, typified by BHT (2,6-di-t-butyl-p-methylphenol), isolated from a resin-made file is adsorbed on the ink-receiving layer of the recording medium when the recording medium is stored in the file, and the phenolic antioxidant adsorbed on the microporous site is oxidized into a yellow oxide with time to cause yellowing. With respect to the yellowing caused by BHT, for example, Non-patent Documents 1, 2, 3 and 4 describe that the phenolic antioxidant is oxidized to form a quinone methide structure, and it is dimerized and further oxidized to produce a yellow compound having a stilbenequinone structure. Patent Document 2 describes a recording medium comprising a sulfur-containing organic acid compound having no mercapto group and a phenolic compound in an ink-receiving layer (containing silica) on a non-water-absorbing support. In this Patent Document, are mentioned sulfur-containing compounds such as thioether compounds, thiourea compounds, disulfide compounds, mercapto compounds, sulfinic compounds and thiosulfinic compounds, phenolic compounds, and hindered amines. However, it only describes those obtained by adjusting the surface pH of a receiving layer to 4.0 with an acid and adding a plurality of additives at the Example level. The yellowing-preventing effect by the Example is insufficient for preventing yellowing.
On the other hand, Patent Document 3 discloses an invention relating to a compound having a structure that a sulfine is connected to phenol, as a light-resisting agent and ozone resistance improver. This Patent Document mentions toluenesulfinic acid and benzenesulfinic acid as examples of general acids for adjusting the pH of ink-jet recording media. However, these acids are not used in Examples of ink-jet recording media having a pH of 3.5 though in a Comparative Example containing no compound according to the above-described invention, toluenesulfinic acid is used in place of this compound. It is clearly described that yellowing cannot be prevented according to the Comparative Example.
Patent Document 1: Japanese Patent Application Laid-Open No. 7-232475;
Patent Document 2: Japanese Patent Application Laid-Open No. 2002-219857;
Patent Document: Japanese Patent Application Laid-Open No. 2004-1354;
Non-patent Document 1: Polymer Degradation and Stability, 50 (1995), 313-317;
Non-patent Document 2: Textile Praxis International, October (1980), 1213-1215;
Non-patent Document 3: Textile Chemist and Colorist, April (1983), Vol. 15, No. 4, 52-56;
Non-patent Document 4: Text. Progr., 15 (1987), 16.